In recent years, the most recently developed class of active agents, i.e. pyrethroids have continuously increased in importance. However, some undesired side effects were also observed during their intense utilization. Due to their contact mode of action, they kill not only the arthropods damaging cultivated plants but frequently the useful entomophages, consuming the arthropods. By decreasing the number of the natural enemies, the rate of repeated multiplication of the pests is enhanced, which may influence the specific use of agents, too. In extreme cases, the excessive and unadvised use of the agents may lead to such a decrease in the number of useful entomophages that, due to the lack of regulation, the agriculturally indifferent arthropods, playing an unimportant role in fauna, may become so-called "man-made" pests (A. W. A. Brown: "Ecology of Pesticides", Wiley-Sons, 1978).
Another problem is connected with the strongly specific action mechanism of pyrethroids causing a higher risk of the development of resistance than is the case with the traditional agents.